I. Field of the Invention
The present invention relates to a method for the selection, preparation and use of oligomers that contain amino acids, and to compositions containing such oligomers. More specifically, the oligomers contain amino acid sequences that are less susceptible to microbial degradation in the rumen as compared to naturally occurring amino acid sequences, and so may be used for supplementing important nutrients to the animals. Moreover, the process disclosed herein may be used to design therapeutic peptides that can complement microbial protein synthesis in the rumen.
II. Description of the Related Art
Ruminants are animals that possess a complex stomach consisting of four morphologically distinct compartments. These compartments are rumen, reticulum, omasum and abomasum. The rumen and the reticulum are fermentation compartments where many species of microorganisms live. Digestion of the feed is conducted primarily by cellulase, amylase, cellobiose, and proteinases which the microflora secrete in the rumen and the reticulum.
One major problem associated with ruminant digestion is that substantial amounts of proteins and amino acids are hydrolyzed and fermented into ammonia and carbon dioxide by the resident microflora of the rumen. This microbial action renders significant amounts of biologically active peptides unavailable for animal absorption. Moreover, dietary supplements that contain essential amino acids are extensively degraded. This degradation renders the supplemented essential amino acids unavailable to the animals. The microbial action also generates excess nitrogen that the ruminants have to dispose of, burdening the secretion system of the animals and contributing to waste disposal problems, especially in high density industrial feeding operations.
Studies have been conducted in search for methods that can effectively protect peptides or amino acids from degradation. One approach has been to modify the peptide or amino acid materials by physical or chemical methods making the materials less susceptible to microbial degradation. In one example, heating soybean meal has been shown to help alleviate the degradation of proteins by microorganisms; however, the parameters of the heating process are difficult to control in order to obtain reliable and repeatable results. Insufficient heating may lead to no protection from degradation, while overheating may cause undesirable biological and/or chemical changes to the peptides or amino acids. Another method includes coating of peptides with shielding materials, such as fat. The coating procedures are tedious, and the side-effects of shielding materials on the body and on the peptides have significantly limited this concept in application. To date, no shielding technologies have proven stable when subjected to feed pelleting procedures.
Yet another approach is to react the amino acid or peptide materials with substituents that render the materials less susceptible to degradation. U.S. Pat. No. 6,605,590 issued to Lorbeit et al. discloses a process for attaching a residue of an α-hydroxy carboxylic acid (e.g., 2-hydroxy-4-(methylthio) butynoic acid (“HMB”) to the end of an amino acid oligomer. The oligomers end-capped by HMB demonstrate reduced cleavage by a variety of proteases, but suffer a disadvantage that the α-hydroxy carboxylic acid may alter the chemical and/or biological characteristics of the peptide. For instance, HMB-poly-lysine is not digested by many proteases that otherwise digest lysine oligomer in the intestine, and so the HMB substitution defeats the purpose of rendering such materials available for adsorption in the intestines. There remains a need for a method of designing and selecting for amino acid oligomers that are resistant to microbial degradation in the rumen but are digestible in the intestine.
Although the HMB-capped oligomers disclosed in U.S. Pat. No. 6,605,590 appear to resist protease degradation in vitro, it is not known whether these oligomers are resistant to microbial degradation in the rumen in vivo. Indeed, experiments on degradation of methionine analogs, such as HMB-methionine, have produced conflicting results. While some studies have concluded that HMB is mostly resistant to microbial degradation, others have shown that merely 5.3% of HMB consumed escapes rumen degradation to reach the omasum. See e.g., Determination of rumen degradability and ruminal effects of three sources of methionine in lactating cows, S. Noftsger et al., J Dairy Sci. 2005 January; 88(1):223-37. Therefore, there is a need for a method to generate amino acid oligomers that can sustain microbial degradation in vivo.